Where can I find B&W film for an Imperial Satellite 127 camera?

A very late update: 127 film is now available, new, in both color and black and white, from Rera (Rerapan, ISO 100 B&W, and Rerachrome, ISO 100 color negative despite the name); it's available from B&H Photo and Film Photography Project.

Frugal Photographer also offers at least two color print emulsions in 127 (this is the Canadian-packaged Bluefire Murano).

My own preference, however, and the reason I'll always have film available for my 127 cameras, is to slit my own 127 from 120.

The cutting can be done in daylight, with a cigar cutter or utility knife (I've done it by rolling a snap-blade extended long on the roll on a smooth table top), or with any kind of sharp, thin blade if you have a means to spin the roll. There are also commercial 3D printed devices to cut the roll (one even respools the film in the process).

You need to ensure you keep the side of the 120 roll with the 6x4.5 framing track, in order to have the 6x6 framing track land under the center 4x6.25 window, and the 6x4.5 track land under the edge 4x4 window in your 127 cameras. For full-frame and half-frame cameras you will also have to mask the frame gate in the camera by a few millimeters to avoid frames overlapping by 4-5 mm (because the 6x6 track has shorter spacing than the original 4x6.25 track on "real" 127 film).

As a bonus, you can use any emulsion available on 120 film, and keep the 120 backing paper (which was cut along with the film); this will get you 16 frames of 4x4 or 12 of 4x6, instead of the 12 or 8 on original 127. And yes, the film and backing will (just) fit on the 127 spool.

I've done this a number of times, and it works fine in every 127 camera I've tried.